Medical devices including a non-polar silicone matrix and a radiation resistant component

ABSTRACT

The disclosure is directed to a sterilized medical device including a non-polymerized blend including a silicone matrix material and a radiation resistant component.

CORRESPONDING APPLICATIONS

The present application claims priority to and is a continuation of U.S.patent application Ser. No. 11/179,030, filed Jul. 11, 2005, entitled“RADIATION RESISTANT SILICONE FORMULATIONS AND MEDICAL DEVICES FORMED OFSAME,” naming inventor Mark W. Simon, which is incorporated by referenceherein in its entirety.

FIELD OF THE DISCLOSURE

This disclosure, in general, relates to radiation resistant siliconeformulations and medical devices formed of same.

BACKGROUND

Polymeric materials are increasingly being used in medical devices. Inparticular, silicone rubbers are being used in applications that rely onflexibility. For example, silicone rubber is used in joint replacementdevices, surgical implants, and surgical stents. Silicone rubbers arealso used in medical equipment used external to a patient's body, suchas fluid flow devices, including tubing, pumps and valves. In each ofthese applications, sterility of the devices and implants is desirable.

Traditional sterilization techniques include autoclaving, includingheating components in the presence of water or steam under pressure.Other typical sterilization techniques include radiation techniques,such as irradiating with gamma radiation. However, some types ofsilicone, and in particular, polyalkylsiloxanes, tend to undergocross-linking during sterilization procedures.

More recently, the medical devices industry has increasingly turned toirradiation procedures for sterilizing medical devices. Irradiativesterilization techniques tend to cause free radical generation innon-polar silicone polymers, such as polyalkylsiloxane. Such freeradical formation leads to additional cross-linking, resulting in achange in physical properties. Moreover, in devices in which twosilicone surfaces are in contact, the free radical formulation andsubsequent cross-linking may lead to a bonding of those surfaces.

Bonding of contacting surfaces is particularly disadvantageous in fluidflow devices, such as cannulas, valves, and duck bill shaped components.In valve configurations in which a slit or overlapping flaps act asvalves, cross-linking may reduce or eliminate the opening and theability to control fluid flow.

Traditional methods to prevent slit or opening surfaces from bondingtogether include application of lubricants and surface coatings on theexterior of the valves and openings. However, such an application ofexterior lubricants introduces a costly and inconvenient step into themanufacturing process. In addition, the medical devices industry isturning to sterilization of prepackaged products, which limit access tothe devices and prevent introduction of lubricants prior to thesterilization process. As such, improved silicone formulations andmedical devices formed of those formulations, as well as, improvedmethods of sterilizing such medical devices would be desirable.

SUMMARY

In a particular embodiment, the disclosure is directed to a sterilizedmedical device including a non-polymerized blend including a siliconematrix material and a radiation resistant component.

In another exemplary embodiment, the disclosure is directed to a medicaldevice including an opening defined by two contacting surfaces formed ofpolymeric material including polyalkylsiloxane and exhibiting a resealperformance not greater than about 3 and post radiation burst pressurenot greater than about 6 psi.

In a further exemplary embodiment, the disclosure is directed to amedical device including a slit opening formed in a polymeric material.The polymeric material includes a non-polar silicone matrix material anda polar radiation resistant component.

In a further exemplary embodiment, the disclosure is directed to asterilized medical device including an opening defined by two contactingsurfaces formed of polymeric material including a non-polymerized blendof non-polar polyalkylsiloxane in a polar radiation resistant component.The polymeric material exhibits a reseal performance not greater thanabout 3 and a post radiation burst pressure not greater than about 6psi.

In another exemplary embodiment, the disclosure is directed to a methodof forming a medical device. The method includes preparing a mixture ofpolyalkylsiloxane precursors and a radiation resistant component to aloading about 0.1 wt % to about 20 wt % of the radiation resistantcomponent based on the weight of the polyalkylsiloxane precursors. Themethod further includes filling a mold with the mixture and curing thepolyalkylsiloxane precursors to form the medical device.

In a further exemplary embodiment, the disclosure is directed to amethod of forming a medical device. The method includes preparing amixture of polyalkylsiloxane precursors and a radiation resistantcomponent having a viscosity not greater than about 70,000 cps. Themethod further includes filling a mold with the mixture and curing thepolyalkylsiloxane precursors to form the medical device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes an illustration of an exemplary embodiment of a medicaldevice.

FIG. 2 includes an illustration of an exemplary embodiment of asilicone-based portion of a medical device, such as the medical deviceillustrated in FIG. 1.

FIGS. 3, 4, and 5 include illustrations of exemplary embodiments ofopenings within a medical device.

FIGS. 6 and 7 include illustrations of exemplary methods of forming amedical device.

FIG. 8 includes an illustration of an exemplary method for using amedical device.

FIGS. 9, 10, 11, 12, and 13 include graphs illustrating the influence ofradiation resistant additives on the properties of siliconeformulations.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION OF THE DRAWING(S)

In one particular embodiment, the disclosure is directed to asilicone-based formulation, which may be used in medical devices thatare sterilized by irradiation. The silicone-based formulation may, forexample, be formed of a non-polar silicone matrix, such as apolyalkylsiloxane matrix, and a radiation resistant component. In oneexemplary embodiment, the radiation resistant component is a polar lowmolecular weight silicone polymer. The radiation resistant component maybe included in the silicone-based formulation in an amount of about 0.1wt % to about 20 wt % based on the weight of the non-polar siliconematrix. Such a silicone formulation may be useful in forming medicaldevices that are sterilized using irradiative techniques, such as gammaradiation techniques. In particular, the silicone formulation may beused in the formation of fluid control devices, such as cannulas,valves, and duck bill shaped components. In one exemplary application,the silicone formulation is used to form needleless intravenous valves.

In another exemplary embodiment, the silicone formulation includes asilicone polymeric matrix. The polymeric matrix may be formed, forexample, using a non-polar silicone polymer. The silicone polymer may,for example, include polyalkylsiloxanes, such as silicone polymersformed of a precursor, such as dimethylsiloxane, diethylsiloxane,dipropylsiloxane, methylethylsiloxane, methylpropylsiloxane, orcombinations thereof. In a particular embodiment, the polyalkylsiloxaneincludes a polydialkylsiloxane, such as polydimethylsiloxane (PDMS). Ingeneral, the silicone polymer is non-polar and is free of halidefunctional groups, such as chlorine and fluorine, and of phenylfunctional groups.

In one embodiment, the silicone polymer is a platinum catalyzed liquidsilicone rubber. Alternatively, the silicone polymer may be a peroxidecatalyzed silicone formulation. The silicone polymer may be a liquidsilicone rubber (LSR) or a high consistency gum rubber (HCR). In oneparticular embodiment, the silicone polymer is an LSR formed from a twopart reactive system. Particular embodiments of LSR include Wacker 3003by Wacker Silicone of Adrian, Mich. and Rhodia 4360 by Rhodia Siliconesof Ventura, Calif. In another example, the silicone polymer is an HCR,such as GE 94506 HCR available from GE Plastics.

The silicone formulation may also include a radiation resistantcomponent. The radiation resistant component is generally un-reactivewith the silicone matrix when exposed to gamma radiation, such as atleast about 20 kGy gamma radiation. For example, the radiation resistantcomponent may be essentially un-reactive with the silicone matrix whenexposed to gamma radiation, such as, for example, forming essentially nocross-link bonds with the silicone matrix during exposure to gammaradiation. In particular, the radiation resistant component issubstantially un-reactive with the silicone matrix when exposed to gammaradiation in an amount at least about 20 kGy, such as at least about 25kGy, at least about 30 kGy, at least about 40 kGy, at least about 47 kGyor more.

In one exemplary embodiment, the radiation resistant component is apolar component. Particular embodiments of the radiation resistantcomponent include polar silicone oils, such as silicone oils includinghalide functional groups, such as chlorine and fluorine, and siliconeoils including phenyls functional groups. Generally, the radiationresistant component is not terminated with reactive functional groups,such as vinyl and methoxy terminating functional groups. For example,the radiation resistant component may include low molecular weighttrifluoropropylmethylsiloxane polymers. In another exemplary embodiment,the radiation resistant component includes low molecular weightpolyphenyl methyl siloxane.

In a further exemplary embodiment, the radiation resistant componentincludes a hydrocarbon component. For example, the radiation resistantcomponent may be a hydrocarbon-based additive, such as a petroletum, aparaffin-based wax, a hydrocarbon-based gel, a hydrocarbon-based oil,Vaseline®, and Amogell (available from Aldrich Chemical).

Typically, the radiation resistant component exhibits a low viscosity atstandard conditions prior to blending within the silicone matrix. Forexample, the radiation resistant component may have a viscosity notgreater than about 70,000 cps, such as not greater than about 20,000cps, not greater than about 10,000 cps. In particular examples, theradiation resistant component exhibits a viscosity not greater thanabout 5,000 cps, such as not greater than about 1000 cps, not greaterthan about 500 cps, or not greater than about 300 cps. In one particularembodiment, the radiation resistant component exhibits a viscosity notgreater than about 100 cps prior to blending with the silicone matrix.The radiation resistant component is also thermally stable, remainingsubstantially intact and not substantially degrading at temperatures atleast about 170° C., such as at least about 200° C.

In one exemplary embodiment, the silicone formulation may be a blend ofthe silicone matrix and the radiation resistant component. Inparticular, the silicone formulation is not a copolymer between theradiation resistant component and the silicone matrix, (i.e., thesilicone matrix is not cross-linked with the radiation resistantcomponent). In general, the radiation resistant component is notsubstantially polymerized with the polyalkylsiloxane. In one particularembodiment, the silicone matrix is loaded with radiation resistantcomponent in amounts of about 0.1 wt % to about 20 wt %. Loading impliesthat the weight percent of radiation resistant component is based on aweight of the silicone matrix component. For example, the polymer matrixmay be loaded with radiation resistant component in amounts about 0.5 wt% to about 10 wt %, such as about 0.5 wt % to about 5 wt %, or about 0.5wt % to about 2 wt %.

Within the silicone matrix, the radiation resistant component mayexhibit migration as measured by migration performance. In oneparticular embodiment, migration performance is determined by the ratioof the coefficient of friction (COF) of a silicone matrix including theradiation resistant component to the coefficient of friction of asilicone matrix without the radiation resistant component. For example,the migration performance may be determined by the formula:

${{Migration}\mspace{14mu}{Performance}} = \frac{{COF}\mspace{14mu}{of}\mspace{14mu}{Matrix}\mspace{14mu}{with}\mspace{14mu}{Radiation}\mspace{14mu}{Resistant}\mspace{14mu}{Component}}{{COF}\mspace{14mu}{of}\mspace{14mu}{Matrix}\mspace{14mu}{without}{\mspace{11mu}\;}{Radiation}\mspace{14mu}{Resistant}\mspace{14mu}{Component}}$The radiation resistant component may, for example, exhibit a migrationperformance not greater than about 0.6, such as about not greater thanabout 0.5, or not greater than about 0.4. In particular, low viscosityradiation resistant components migrate to the surface of the siliconeformulation and prevent cross-linking between surfaces.

Radiation resistant components may also be selected that have limitedimpact on physical properties of the silicone matrix. For example,radiation resistant components may be selected such that they havelimited impact on physical properties, such as tensile strength, tearstrength, elongation, and durometer. In particular, low molecular weightfluorinated silicones or phenyl silicones are selected that have limitedimpact on the physical properties of the polymer matrix, depending onloading. With loadings not greater than about 10%, such as not greaterthan about 5%, or not greater than about 1%, the radiation resistantcomponent may impact the physical property by less than 20%, such as notgreater than 15%, or not greater than 10%. For example, a loading offluorinated silicone in a polyalkylsiloxane matrix, such aspolydimethylsiloxane, in amounts not greater than 5% impacts tensilestrength of the silicone formulation by not greater than 15% and aloading of phenyl silicone impacts the silicone formulation by notgreater than 20%. In a further example, loading fluorinated silicones orlow molecular weight phenyl silicones in amounts not greater than 5 wt %impact tear strength by not greater than 15%, such as not greater than10%. In a further exemplary embodiment, loadings not greater than 5% offluorinated silicone or phenyl silicone affects elongation properties bynot greater than 15%. Such loadings of fluorinated or phenyl siliconesin amounts not greater than 5% affects hardness properties, such asShore A hardness, by not greater than 10%.

Particular embodiments of the radiation resistant component are approvedfor use in medical applications. For example, the radiation resistantcomponent may be approved for use internal to a patient, short-terminternal use, or use external to a patient.

The silicone formulation may be especially useful for use in medicaldevices. In a particular embodiment, a sterilized medical deviceincludes a non-polymerized blend of a silicone matrix and a radiationresistant component. Here, “non-polymerized” denotes the radiationresistant component not being appreciably polymerized with the matrix,although the matrix itself is generally deployed in the context of amedical device as a polymerized polymer and the radiation resistantcomponent may be a low molecular weight polymer. The medical device may,for example, include an opening defined by two contacting surfacesformed from the silicone matrix material. FIG. 1 includes anillustration of an exemplary embodiment of a medical device, such as afluid control device 100. In one particular embodiment, the fluidcontrol device includes a silicone-based portion 114 that isencapsulated inside a two-component housing including valve casing 104and fluid directional component 102. The fluid directional component 102includes openings 106 and 108 for engaging tubing. The openings 106 and108 and silicone component 114 are fluidically connected via a hollowchamber (not shown). The valve casing 104 may also include an engagementstructure 112 configured to engage a needleless syringe or other fluidflow devices. In addition, the housing 104 may include an opening 110through which silicone based valve portion 114 is exposed.

Generally, when fluid is directed into the device 100 via the opening106 or the opening 108, the fluid is prevented from exiting via opening110. However, fluid directed into the device 100 via opening 110 ispermitted to flow into the chamber connecting the openings 106 and 108when a specific pressure differential is exerted on the silicone valveportion 114. In another embodiment, the valve portion 114 may permitflow out of opening 110 and prevent flow from opening 110 into thedevice 100. Alternatively, the valve portion 114 may be a two way valve,permitting flow in either direction based on the value of the pressuredifferential exerted across the valve portion 114.

Turning to FIG. 2, a silicone-based valve portion 202 is illustratedthat includes a valve surface 204 and an opening 206. The silicone-basedvalve portion may also include a lip 208 configured to engage a housing(not shown). In one particular embodiment, the valve portion 204includes a flap or a slit that provides an opening for fluid flow whenpressure or mechanical force is applied across the valve surface.

In one particular embodiment, the silicone formulation may be used toform components of valves, such as the valves of U.S. Pat. No. 6,039,302issued to Cote, Sr. et al., Mar. 21, 2000, and the valves of U.S. Pat.No. 5,775,671 issued to Cote, Sr., Jul. 7, 1998.

For example, FIG. 3 illustrates a valve surface 302 that includes anopening or a slit 304. When pressure is applied to one side of thevalve, or a pressure differential is applied across the valve, theflexibility of the silicone-based portion allows the slit 304 to open,permitting fluid flow.

FIGS. 4 and 5 include cross-sectional illustrations of exemplaryembodiments of a valve opening. For example, the valve opening 400includes a cut or slit across the valve material that results inopposing surfaces, such as surfaces 402 and 404, that contact when thevalve is in a closed position. In another example illustrated in FIG. 5,the valve opening 500 comprises flaps that overlap resulting incontacting surfaces, such as surfaces 502 and 504, which contact whenthe valve is in a closed position. Under sterilization conditions, thepresent silicone formulation limits or reduces cross-linking between thecontacting surfaces.

The performance of the silicone formulations when used in medicaldevices, such as valves, may be expressed in reseal performance. Resealperformance is a ratio of burst pressure of a sterilized valve to burstpressure of the valve prior to sterilization. For example, resealperformance may be determined by the formula:

${{Reseal}\mspace{14mu}{Performance}} = \frac{{Sterilized}\mspace{14mu}{Burst}\mspace{14mu}{Pressure}}{{Pre}\text{-}{Sterilized}\mspace{14mu}{Burst}\mspace{14mu}{Pressure}}$Burst pressure expresses the differential pressure exerted across avalve to open the valve. Sterilization may be performed in an autoclaveor by irradiating, for example, with gamma radiation. Sterilization ofthe silicone material described above results in valves having poststerilization burst pressures not greater than about 7 psi, such as notgreater than about 6 psi, not greater than about 5 psi, or not greaterthan about 3.5 psi. In particular embodiments, the reseal performance ofthe valve is not greater than about 3, such as not greater than about2.5, not greater than about 2.0, or not greater than about 1.5.Particular embodiments of medical device valves using the abovedescribed silicone formulation have reseal performance not greater thanabout 3 and final post-sterilization burst pressures not greater thanabout 6.

The medical device may be formed by a method 600, illustrated in FIG. 6.The method 600 includes preparing of a mixture of silicone precursorsand the radiation resistant component, as illustrated at 602. Forexample, alkylsiloxane monomer, such as dimethylsiloxane, may be mixedwith the radiation resistant component. The mixture may further includecatalysts and other additives. To form a silicone-based portion of amedical device, a mold is filled with the mixture, as illustrated at604, and the alkylsiloxane monomers are cured, as illustrated at 606.However, the radiation resistant component does not substantiallypolymerize and does not substantially cross-link or react with thealkylsiloxane precursors.

Once cured, the medical device may undergo additional curing orpost-curing, such as through thermal treatments, as illustrated at 608.For example, the medical device may be treated at temperatures at leastabout 170° C. such as least about 200° C.

To further prepare the medical device for use, the valve opening may beformed and the device may be assembled, packaged and sterilized, asillustrated in method 700 of FIG. 7. For example, the method 700includes forming an opening in a silicone portion of the medical device,as illustrated at 702. The opening may, for example, be formed throughcutting, slicing, or punch cutting a slit in a surface of the material.Alternatively, the valve portion of the medical device may be formed byoverlapping two opposing silicone surfaces.

The medical device is assembled, as illustrated at 704. For example, asilicone based valve portion of the medical device may be inserted intohousings, such as polycarbonate housings. In alternative embodiments,the valve openings may be formed after assembly of the medical device.In another embodiment, the silicone-based portion may substantially formthe complete medical device.

Optionally, the medical device may be packaged, as illustrated at 706.For example, the medical device may be sealed in individual packagesprior to sterilization. Alternatively, the medical devices may be placedin boxes in preparation for shipping prior to sterilization.

The medical devices are sterilized, as illustrated at 708. In oneparticular embodiment, the medical devices are irradiated with gammaradiation. For example, the medical devices may be irradiated with atleast about 20 kGy, such as about 25 kGy, at least about 40 kGy, or atleast about 47 kGy gamma radiation. In particular, the medical devicesare irradiated without the application of external lubricants. As such,the medical devices are generally free of separately and externallyapplied lubricants.

In use, the medical devices may be coupled to a fluid flow path, asillustrated at 802 of method 800 of FIG. 8. The method 800 furtherincludes directing medicinal fluids through the medical device, asillustrated at 804. In a particular embodiment, the medical device maybe a needleless intravenous valve allowing the direction of medicinalfluids into an infusion tube. Alternatively, the valve may permit thewithdrawal of blood through the tube.

Particular embodiments of the above disclosed medical devicesadvantageously exhibit low failure rates. Failure denotes resealing of avalve or duck-bill shaped device during sterilization or during a postcure process. Post cure processing generally refers to performance ofadditional curing, often by subjecting a cured product to elevatedtemperatures. Particular embodiments of the silicone formulation whenused in medical devices exhibit post sterilization failure rates notgreater than 10%, such as not greater than about 9% or not greater thanabout 5%.

EXAMPLES

Low molecular weight polar siloxane fluids are tested as gamma radiationresistant additives in liquid silicone rubber (LSR). Formulationsinclude a two part LSR system having part A including a platinum basedcatalyst and a vinyl based rubber and part B including a hydridecross-linking agent, a catalyst inhibitor and a vinyl based rubber.About 300 grams of LSR part A and 300 grams of LSR part B and a specificamount of gamma radiation resistant additive are mixed in a five quartbowl using a Kitchen-Aid mixer on a low setting for twelve minutes undervacuum (25 inHg). In particular, a gamma radiation resistant additive,such as a polytrifluoropropylmethylsiloxane from manufacturers, such asGelest (FMS-121 and FMS-123) and NuSil (MED 400 and MED 400-100); or apolyphenylmethylsiloxane by Gelest (PMM-0025) and NuSil (S-7400) areadded. The mixer is stopped at four-minute intervals to scrape downsilicone off the walls of the mixing pan. Mixing is resumed and allowedto continue under vacuum for a total of twelve minutes. Seventy grams ofblended silicone rubber is placed onto Mylar sheets coated withmold-release solution (i.e., water, IPA, and surfactant). The rubber ispressed to approximately fill the mold cavity. The mold is closed andloaded into a 166° C. pre-heated press and immediately pressure isapplied to the mold (25 tons) to avoid scorching. The material was curedunder pressure at a temperature for five minutes. The molded part isremoved from the mold and post-cured in a box oven for four hours at177° C.

The radiation resistant additives are tested for physical propertyinfluence, migration performance and reseal performance understerilization conditions. Sterilization is performed using irradiationwith gamma rays from a 60 CO-source and a minimum dose of 47 kGy.Physical properties are tested using ASTM test method D-412 for tensilestrength, elongation modulus, and Young's modulus; ASTM test methodD-624 for tear strength; and ASTM test method D-2240 for durometer(Hardness Shore A).

To evaluate conditions of slits, a burst pressure test is developed toquantify the amount of force required to open the slit. The air pressureused to open the slit quantifies the extent of slit reseal followinggamma irradiation. Higher burst pressures represent a more severe slitreseal condition. The reseal test includes uniformly slitting discs andplacing the discs into a grooved housing over a pressure chamber. Thediscs are cut from ASTM slabs of gamma radiation resistant formulationsand are prepared using a one inch die to cut test specimens from a 6×6inch slabs having an approximate thickness of 0.077 inches. Uniformityof the slit dimensions aids in generating consistent data. The slits areformed using a razor blade having a length of 0.35 inches by 0.012inches width mounted to a durometer stand and cutting a slit into theone inch discs. A two-pound weight is placed into a spring loadeddurometer head to provide consistent force during the cut.

To determine burst pressure, a pressure gauge is used to record theburst pressure of the specimen. Burst pressure is defined as the minimumpressure required to open the slit and prevent further increases in therecorded pressure as air pressure is introduced into the chamber. Airpressure is adjusted continuously until bursting.

Migration performance is measured using coefficient friction.Coefficient of friction measurements were performed using a Falex Wearand Friction tester. A one-pound load is used at a rotational rate of 50rpm.

Example 1

The physical properties of silicone formulations includingfluorosilicone and phenyl silicone are tested relative to a standardfree of gamma radiation resistant additives. FIG. 9 illustrates theinfluence of gamma radiation resistant additives on tensile strength.When approximately 1 wt % gamma radiation resistant additive is includedin the silicone formulation, relatively little change is noted in thetensile strength of the samples. Higher concentrations (approximately 5wt %) phenylsilicone have a greater influence on tensile strength.However, the influence is less than about 20%.

As illustrated in FIG. 10, fluorosilicone and phenylsilicone affectelongation properties of silicone formulations, slightly increasing theelongation properties. However, the influence is not greater than about15%.

As illustrated in FIG. 11, fluorosilicone and phenylsilicone onlyslightly affect tear strength properties of silicone formulations. Oneweight percent fluorosilicone additive increases tear strength slightly,while 5 wt % decreases tear strength slightly. Generally, the influenceis not greater than about 15% and is typically not greater than about10%.

FIG. 12 illustrates the influence of fluorosilicone and phenylsiliconeadditives on durometer, as measured in Shore A hardness. The effect ofthe additives is not greater than about 10%.

Example 2

Migration performance of additives is influenced by the viscosity of thepure additive component prior to mixing into the silicone formulation.FIG. 13 illustrates the coefficient of friction for additives havingdifferent viscosity. High viscosity (>10,000 cps) fluorosilicone andphenylsilicone additives have higher coefficients of friction than lowviscosity (<1000 cps) additives. In fact, the migration performance ofhigh viscosity fluorosilicone is nearly 1, while the migrationperformance of low viscosity fluorosilicone is not greater than about0.6. The migration performance of low viscosity phenylsilicone is notgreater than about 0.5, and, in some embodiments, is less than 0.4.

Example 3

Reseal performance of additives is influences by the type of additive,loading of the additive, and properties of the additive. Resealperformance is the ratio of post-irradiation burst pressure topre-irradiation burst pressure. As such, low reseal values aredesirable. TABLE 1 illustrates the influence of additives on burstpressure and reseal performance. A set of ten to thirty samples areprepared for each formulation and reseal performance tests are performedon each of the samples. TABLE 1 illustrates the average performance ofeach of the formulations. The standard represents samples withoutadditive and the STD-lubed represents samples without additive and withexternally applied lubricant. In general, the additives in variousconcentrations result in samples with reseal performance close to orbetter than the standard sample. In some examples, the additives resultin samples with reseal performance close to the STD-lubed sample.

TABLE 1 INFLUENCE OF ADDITIVES ON RESEAL PERFORMANCE Burst Initial BurstLoading psi Final psi Reseal Additive wt % (Ave 10) (Ave 10) PerformanceStandard 0% 3.55 8.88 2.5 STD-Lubed Lube 5% 3.27 3.27 1 Fluoro, 100 cps0.5%   2.71 5.70 2.10 Fluoro, 100 cps 1% 2.99 4.72 1.57 Fluoro, 100 cps2% 2.38 5.35 2.24 Fluoro, 100 cps 5% 2.44 5.63 2.30 Fluoro, 300 cps 10% 3.13 7.09 2.26 Fluoro, 300 cps 12%  2.42 4.9 2.02 Fluoro, 300 cps 20% 2.61 2.74 1.04 Phenyl, 1000 cps 0.5%   2.28 5.40 2.37 Phenyl, 1000 cps1% 2.10 3.37 1.60 Phenyl, 1000 cps 2% 2.31 3.44 1.49 Phenyl, 1000 cps 5%2.4 3.12 1.30 Phenyl, dimethyl 10%  2.2 6.38 2.9 Fluoro, methylvinyl10%  2.84 7.12 2.5

TABLE 2 illustrates the influence of additive viscosity on burstpressure and reseal performance. Samples include fluorosiliconeadditives having different viscosity. Samples having low viscosityadditives generally have low values, and thus improved resealperformance. Based on models estimated from the data, additives havingviscosity not greater than about 70,000 cps exhibit improved resealperformance. TABLE 3 illustrates the influence of additive loading onburst pressure and reseal performance. Reseal performance appears, forsome exemplary additives, to be independent of loading. Generally, boththe pre-irradiation and post irradiation burst pressures are reducedwith increasing concentrations of additive. TABLE 4 illustrates theburst pressure and reseal performance for different species of additive.Fluorosilicone additives at 5% loading tend to have a higher ratio ofburst pressures and, thus a lower reseal performance thanphenylsilicone.

TABLE 2 INFLUENCE OF VISCOSITY ON RESEAL PERFORMANCE Burst Initial BurstFinal psi psi Reseal Viscosity (Ave 10) (Ave 10) Performance Standard3.55 8.88 2.5   100 2.69 4.2 1.56 10,000 2.72 5.6 2.05 100,000  3.298.62 2.62

TABLE 3 INFLUENCE OF LOADING ON RESEAL PERFORMANCE Burst Initial BurstFinal psi psi Reseal Loading (Ave 10) (Ave 10) Performance Standard 3.558.88 2.5 1% 2.49 2.69 1.08 5% 2.17 2.34 1.07 10%  1.84 2.01 1.09

TABLE 4 RESEAL PERFORMANCE FOR SPECIES OF ADDITIVE Burst Initial BurstFinal psi psi Reseal Molecule (Ave 10) (Ave 10) Performance None 3.558.88 2.5 Fluoro 2.69 4.2 1.56 Phenyl 2.6 2.87 1.1

Example 4

Vaseline® is substituted for low molecular weight polar siloxane fluidsin a silicone matrix that is formed as described above. TABLE 5illustrates the effect of Vaseline® loading on burst pressure and resealperformance. The Vaseline® additive provides desirable resealperformance, even when subjected to a post curing. In general,hydrocarbon-based additive, such as Vaseline®, provides greaterimprovement in reseal performance in device manufacturing processes thatdo not include post curing.

TABLE 5 RESEAL PERFORMANCE FOR PETROLETUM ADDITIVE Burst Initial BurstFinal psi psi Reseal Loading (Ave 10) (Ave 10) Performance   1% 2.492.69 1.08   5% 2.34 2.17 0.927  10% 1.84 2.01 1.09 0.5% PC 2.13 7.103.33   1% PC 2.12 6.32 2.98   5% PC 2.91 4.53 1.56 PC—Post Cured

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true scope of the present invention. Thus, to the maximum extentallowed by law, the scope of the present invention is to be determinedby the broadest permissible interpretation of the following claims andtheir equivalents, and shall not be restricted or limited by theforegoing detailed description.

What is claimed is:
 1. A sterilized medical device comprising anon-polymerized blend including a non-polar silicone matrix material anda radiation resistant component dispersed in the non-polar siliconematrix material, the radiation resistant component comprising a polarsilicone oil.
 2. The sterilized medical device of claim 1, wherein thenon-polymerized blend comprises a loading of radiation resistantcomponent of about 0.1 wt% to about 10 wt% based on the weight of thesilicone matrix material.
 3. The sterilized medical device of claim 2,wherein the loading of the radiation resistant component is about 0.5wt% to about 10 wt%.
 4. The sterilized medical device of claim 1,further comprising first and second surfaces in separable contact witheach other, the first and second surfaces formed of the non-polymerizedblend.
 5. The sterilized medical device of claim 1, wherein thesterilized medical device includes an internal passageway for passage ofa fluid therethrough.
 6. The sterilized medical device of claim 1,wherein the sterilized medical device is a fluid control device.
 7. Thesterilized medical device of claim 1, wherein the radiation resistantcomponent is substantially non-reactive with the silicone matrixmaterial.
 8. The sterilized medical device of claim 7, wherein theradiation resistant component is substantially non-reactive with thesilicone matrix material when exposed to at least about 25 kGy gammaradiation.
 9. The sterilized medical device of claim 1, wherein theradiation resistant component comprises fluorosilicone oil.
 10. Thesterilized medical device of claim 1, wherein the radiation resistantcomponent comprises phenylsilicone oil.
 11. The sterilized medicaldevice of claim 1, wherein the sterilized medical device exhibits areseal performance not greater than about
 3. 12. The sterilized medicaldevice of claim 11, wherein a post radiation burst pressure is less thanabout 6 psi.
 13. The sterilized medical device of claim 1, wherein theradiation resistant component exhibits a migration performance notgreater than about 0.6.
 14. A medical device comprising: a slit openingformed in a polymeric material comprising a non-polar silicone matrixmaterial blended with 0.1 wt% to 20 wt% of a polar radiation resistantcomponent comprising fluorosilicone oil or phenylsilicone oil, the polarradiation resistance component having a premix viscosity of not greaterthan 70000 cp.
 15. The medical device of claim 14, wherein the medicaldevice is a needless intra-venous injection valve.